Vehicle occupant proximity sensor

ABSTRACT

A vehicle occupant proximity sensor includes a transmitting electrode in a vehicle seat and an array of receiving electrodes mounted in a vehicle headliner above the vehicle seat. The sensor determines the capacitance at each of the receiving electrodes, which varies based upon the proximity of the occupant to each receiving electrode, thus producing an array of proximity information indicating in two dimensions the position of the occupant.

[0001] This application is a continuation of U.S. Ser. No. 09/872,873filed Jun. 1, 2001, now U.S. Pat. No. ______, which claims priority toU.S. Provisional Serial No. 60/236,848 filed Sep. 29, 2000.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to a vehicle occupant safetysystems, and more particularly, to a vehicle occupant proximity sensorfor use with a vehicle occupant safety system.

[0003] Vehicle occupant safety systems that are activated in response toa vehicle crash for purpose of mitigating occupant injury are well knownin the art. A vehicle may contain automatic safety restraint actuatorssuch as front and side air bags, seat belt pretensioners, and deployableknee bolsters. The occupant protection system may further include acollision/crash sensor for sensing the occurrence of a vehicle crash andfor providing an electrical signal indicative of the crash severity.

[0004] Several known occupant protection systems include an occupantposition sensor that senses the position of the occupant with respect toan associated inflatable protection module. The occupant position sensorfor such a system could be an ultrasonic sensor, an infrared sensor, anda capacitive sensor, and/or a weight sensor. A controller, which isconnected to the sensors, controls the inflatable protection module inresponse to the sensed position of the occupant. In response to thesensed occupant position, one or more deployment aspects of the air bagmay be adjusted. A protection system with adjustable aspects ofdeployment is commonly referred to as an “adaptive” protection system.Specifically, if the occupant is positioned in a position such thatdeploying the air bag will not enhance protection of the occupant, itmay be desirable to suppress actuation of the occupant protectionmodule. An occupant who is very near the protection module is referredto as being within an occupant out-of-position zone. Deploying the airbag for an occupant who is within the occupant out-of-position zone maynot enhance protection of the occupant.

[0005] In any case the determination of occupant's position is animportant part of adaptive occupant protection system. There are severaltypes of proximity sensors, such as ultrasonic sensor, a video sensor, acapacitive sensor, and an infrared sensor. Different obstacles such as amap, a book, or a newspaper could occlude signals from ultrasonic andvideo sensors. A lighter or cigarette could blind an infrared sensor.Existing capacitive sensors rely on the strength of the electric fieldto determine proximity (i.e. dash mounted capacitive sensor). This makesthe sensor susceptible to being fooled if the strength of the electricfield is blocked. A system that relies on the strength of the electricfield may be inaccurate if a portion of the signal is lost. Furthermore,existing sensors are also complex and expensive.

[0006] This invention is based on a simple fact—the physical propertiesof the human body do not change rapidly. For example, the conductivityof the human body tends to be constant and hence it can be used tomeasure the distance between the occupant and the correspondingprotection module through the use of a capacitive sensor.

SUMMARY OF THE INVENTION

[0007] The present invention provides an occupant proximity sensorutilizing an occupant's conductivity to determine proximity by measuringthe capacitance between the occupant's head and roof-mounted array ofsensors (electrodes).

[0008] A transmitting electrode is mounted in a vehicle seat. An arrayof receiving electrodes is mounted to the ceiling of the vehicle abovethe occupant's seat. A control unit serially switches these receivingelectrodes to create a profile of the produced electric field. Desiredprecision is achieved by counting the proximity for each element in thearray. The resulting data indicates in two dimensions the accurateposition of the occupant in the passenger compartment. The control unitutilizes an excitation method and a synchronous detection method tomeasure capacitance. It uses micro power low frequency signal that issafe for human.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Other advantages of the present invention will be readilyappreciated as the same becomes better understood by reference to thefollowing detailed description when considered in connection with theaccompanying drawings wherein:

[0010]FIG. 1 illustrates the vehicle occupant proximity sensor installedin a vehicle passenger compartment with an occupant safety system.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0011]FIG. 1 illustrates a vehicle occupant proximity sensor 10 fordetermining the position of an occupant 12 in a vehicle seat 14, andmore particularly, for determining the position of the occupant's head15. The occupant 12 and vehicle seat 14 are installed in a vehiclepassenger compartment 16 having an occupant safety system, including anautomatic safety restraint, such as an airbag 18. Although a steeringwheel mounted airbag 18 is illustrated as an example, it should also beunderstood that the present invention is also useful for side airbags,seatbelt pretensioners, deployable knee bolsters, and any otherautomatic safety restraint actuators. Crash detector 19, such as a crashsensor of any known type, is used to determine the occurrence of avehicle crash and to determine the crash severity.

[0012] The vehicle occupant proximity sensor 10 comprises a transmittingelectrode 20 generating an electromagnetic signal and a receivingelectrode array 22 comprising a plurality of receiving electrodes 22 a-narranged in an array, for receiving the electromagnetic signal generatedby the transmitting electrode 20. A control unit 24 receives electricalsignals from the receiving electrode array 22 based upon theelectromagnetic signal received by the electrode array 22. The controlunit 24 also receives a signal from seat track position sensor 26indicating the position of the vehicle seat 14 on a vehicle track (notshown) in the passenger compartment 16.

[0013] The transmitting electrode 20 is mounted in the base of vehicleseat 14. The transmitting electrode 20 may comprise a coil of wire or acopper sheet and can be made from any conductive material, butpreferably comprises a mesh of copper wires approximately one inchapart. Generally, it is preferred to cover a large area of the base ofthe seat 14 with the transmitting electrode 20 and to wrap thetransmitting electrode around the front of the seat. It should beinsured that the transmitting electrode is not shorted to ground via theframe of the vehicle. A frequency generator 27 generates a 10 KHz signalto the transmitting electrode 20, which is then transmitted as anelectromagnetic signal in the passenger compartment 16.

[0014] The receiving electrode array 22 is mounted in the vehicleheadliner 28 in the passenger compartment 16 above the occupant 12. Thereceiving electrodes 22 a-n each comprise a small conductive surface,preferably a 6.5 cm by 9 cm piece of printed circuit board. Thereceiving electrode array 22 is connected to the control unit 24 via amultiplexer 29 and amplifier 30. Again, it must be insured that none ofthe receiving electrodes 22 a-n are shorted to ground via the frame. Themultiplexer 29 enables the control unit 24 to sequentially read valuesfrom the receiving electrodes 22 to determine the position of theoccupant 12.

[0015] The control unit 24 generally comprises a CPU 31 having memory32. The CPU 31 is suitably programmed to perform the functions describedherein and any person of ordinary skill in the art could program the CPU31 accordingly and supply any additional hardware not shown but neededto implement the present invention based upon the description herein.

[0016] In operation, the control unit 24 controls generator 27 togenerate a 10 KHz signal to the transmitting electrode 20. Thetransmitting electrode 20 transmits a 10 KHz signal as anelectromagnetic wave inside the vehicle passenger compartment 16. Theelectromagnetic signal passes through occupant 12 and is received by areceiving electrode array 22. The signal received by each receivingelectrode 22 a-n is based upon the capacitance between it and thetransmitting electrode 22, which in turn will vary depending upon theproximity of the occupant 12 to each receiving electrode 22 a-n.

[0017] The receiving electrode array 22 may be one-dimensional, thusindicating only the distance of the occupant 12 from the airbag 18 alongthe longitudinal axis of the vehicle. However, the electrode array 22 ispreferably two-dimensional as shown in FIG. 1, thus providinginformation regarding the position of the occupant 12 in two dimensionsin the vehicle passenger compartment 16, namely, along the longitudinaland lateral axes of the vehicle. The lateral position information can beused to determine whether to activate side air bags or the force fordeployment of the side air bags, or can also be used for activation ofthe steering wheel mounted air bag 18. The size and resolution of thereceiving electrode array 22 may vary for different applications anddifferent vehicles; however, for one application the receiving electrodearray 22 is preferably 8×8.

[0018] The control unit 24 controls multiplexer 29 to sequentially readeach of the receiving electrodes 22 a-n. Although performedsequentially, it is performed sufficiently quickly relative to normalmotion of a vehicle occupant 12 to provide what is effectively aninstantaneous two-dimensional snapshot of the position of the occupant12 in the passenger compartment 16.

[0019] The values read by control unit 24 are represented graphically asa three-dimensional graph 34 in FIG. 1. As can be seen in FIG. 1, thecapacitance at each receiving electrode 22 a-n depends on the proximityof the occupant 12 to each receiving electrode 22 a-n. Thus, the highestcapacitance will be measured at the receiving electrode closest to head15 of the vehicle occupant 12. Since the vehicle occupant proximitysensor 10 of the present invention provides an array of proximityvalues, this array of information can be processed as an image, as canbe seen in the graph 34. The position of the occupant's head 15, and tosome extent, the position of the occupant's shoulders can be discernedfrom the graph 34 by the control unit 24.

[0020] It should be noted that in determining the position of the head15 of the occupant 12, the values from each receiving electrode 22 a-nare compared to each other, rather than evaluating their absolutevalues. Therefore, the information from the receiving electrode array 22is preferably processed as an image, using known image processingtechniques. Further, the control unit 24 monitors the information fromthe receiving electrode array 22 over time. For example, the position ofthe head 15 of occupant 12 cannot change instantaneously; it must followa path from one point to another. The control unit 24 may additionallyuse the magnitude of the sensor signals to determine the height ofoccupant 12 (but, again, preferably not for determining the position ofoccupant 12). The control unit 24 may additionally take information fromthe vehicle seat track sensor 26, which indicates the position of thevehicle seat 14 on a vehicle seat track.

[0021] All of this information is utilized by control unit 24 todetermine whether to deploy the airbag 18 (or other safety restraintdevice) based upon a crash detected by crash detector 19 and theseverity of a crash. For example, if the control unit 24 determines,based upon information from receiving electrode array 22, that theoccupant 12 is too close to airbag 18, the control unit 24 may determinenot to activate airbag 18 in the event of a crash, or the control unit24 may determine that airbag 18 should be deployed with less force. Onthe other hand, if occupant 12 control unit 24 determines based uponinformation from receiving electrode array 22 that occupant is at adistance from airbag 18 in excess of a predetermined threshold, thecontrol unit 24 will cause airbag 18 to deploy, or will cause airbag 18to deploy with higher force, depending upon the severity of the crash asdetermined by crash detector 19.

[0022] Additionally, information from seat track sensor 26 may beutilized with the proximity information to determine whether and/or howairbag 18 should be deployed. For example, if seat track sensor 26indicates that the vehicle seat 14 is adjusted forward in the vehiclepassenger compartment 16, and the receiving electrode array 22 indicatesthat the occupant 12 is also forward, the control unit 24 may determinenot to deploy airbag 18 in the event of a crash. On the other hand, ifthe seat track position sensor indicates that the vehicle seat 14 is toofar forward, the control unit 24 may decide not to deploy airbag 18,even though the receiving electrode array 22 indicates that the head 15of the occupant 12 is sufficiently rearward for deployment. This wouldoccur in the event that the occupant 12 has the vehicle seat 14 reclinedsignificantly. Further, the control unit 24 may determine that if thehead 15 of the occupant 12 is sufficiently rearward, the airbag 18 maybe deployed in the event of a crash even though the vehicle seat trackposition sensor 26 indicates that the vehicle seat 14 is too farforward. This would indicate that the occupant 12 again has the vehicleseat 14 reclined significantly and sufficiently that the airbag 18should be deployed. Generally, those of ordinary skill in the art willprogram control unit 24 utilizing the above and many additional rulesfor whether to fire airbag 18, and for a multiple stage airbag 18, howmuch force airbag 18 should be deployed. The present invention providesadditional information to the control unit 24, such that those ofordinary skill in the art could take in this additional information toproperly determine whether and with how much force to activate airbag18.

[0023] As explained above, the information from receiving electrodearray 22 is preferably processed as an image and is monitored over time.For example, the position of the head 15 of occupant 12 cannot changeinstantaneously. This principal is utilized to properly handle thesituation where the occupant 12 may touch the headliner 28 with hishand. In this case, the position of the head 15 will have beenidentified by the control unit 24 over time and the hand of occupant 12touching the headliner 28 will appear as a sharp, sudden spike. Bytracking the position of the head 15 of occupant 12 over time, thecontrol unit 24 will properly ignore the sharp, sudden spike from theoccupant's hand, since the head 15 of the occupant 12 cannot moveinstantaneously. Further, since the hand of the occupant 12 will haveless mass than the head 15 of the occupant 12, the shape of the spikewill be sharper than that of the shape of the signal from the head 15,thus also assisting the control unit 24 in distinguishing a hand from ahead. This is true even though the signal may be strongest at thereceiving electrode 22 a (for example) directly above where the occupant12 touches the headliner 28.

[0024] In accordance with the provisions of the patent statutes andjurisprudence, exemplary configurations described above are consideredto represent a preferred embodiment of the invention. However, it shouldbe noted that the invention can be practiced otherwise than asspecifically illustrated and described without departing from its spiritor scope.

What is claimed is:
 1. A method for activating a vehicle occupant safetysystem including the steps of: a. Determining a position of a head ofthe occupant relative to the safety system; and b. Determining whetherto activate the vehicle occupant safety system based upon said step a.2. The method of claim 1 wherein said step a. further includes the stepof measuring capacitance of the head.
 3. The method of claim 2 whereinsaid step a. further includes the step of measuring capacitance at eachof a plurality of points to determine the position of the head in saidstep a.
 4. The method of claim 1 wherein said step a. further includesthe step of receiving an electromagnetic signal at a plurality of pointsin a headliner of a vehicle.
 5. The method of claim 1 further includingthe step of: c. determining the position of the head in said step a. foreach of a plurality of sequential times; d. analyzing the position ofthe head over time based upon said step c.; and e. performing said stepb. based upon said step d. over time.
 6. A method for activating avehicle occupant safety system including the steps of: a. Measuringcapacitance at each of a plurality of points in a vehicle passengercompartment having an occupant safety system; b. Determining a positionof an occupant relative to the safety system based upon said step a; andc. Determining whether to activate the vehicle occupant safety systembased upon said step a.
 7. The method of claim 6 wherein said step a.further includes the step of transmitting an electromagnetic signal froma vehicle seat in the vehicle passenger compartment.
 8. The method ofclaim 7 wherein said step a. further includes the step of measuringcapacitance based upon the electromagnetic signal received at theplurality of points.
 9. The method of claim 6 wherein said step a.further includes the step of measuring capacitance at an array of theplurality of points.
 10. The method of claim 9 wherein said step a.further includes the step of comparing the capacitance measured at eachof the plurality of points with each other.
 11. The method of claim 10wherein the plurality of points are adjacent a headliner in the vehiclepassenger compartment.
 12. The method of claim 11 wherein said step a.further includes the step of: d) monitoring a change in capacitance overtime at the plurality of points; and e) in said step c), determiningwhether to activate the vehicle occupant safety system based upon saidstep d).
 13. A method for activating a vehicle occupant safety systemincluding the steps of: a. Sensing a proximity of an occupant from eachof a plurality of points in a vehicle passenger compartment having anoccupant safety system; and b. Determining a position of an occupantrelative to the safety system based upon said step a.
 14. The method ofclaim 13 further including the step of: c. determining whether toactivate the vehicle occupant safety system based upon said step a. 15.The method of claim 14 further including the step of: d. determining aposition of a seat in the vehicle passenger compartment; and e.determining whether to activate the vehicle occupant safety system insaid step c. based upon said step d.
 16. The method of claim 13 whereinthe plurality of points are an array of said plurality of points. 17.The method of claim 13 further including the step of comparing each ofthe plurality of points to determine position in said step b.
 18. Themethod of claim 13 further including the step of analyzing the array ofsaid plurality of points as an image.
 19. A vehicle passengercompartment proximity sensing system comprising: A capacitive sensorarray measuring capacitance at a plurality of points in a passengercompartment; and A controller determining a position of an occupantbased upon the capacitance measured at the plurality of points.
 20. Thevehicle passenger compartment proximity sensing system of claim 19further comprising: A first electrode generating an electromagneticsignal; Said capacitive sensor array comprising a plurality of secondelectrodes receiving the electromagnetic signal; and the controllerdetermining capacitance at each of the second electrodes to determinethe position of the occupant in the vehicle passenger compartment. 21.The vehicle passenger compartment proximity sensing system of claim 20wherein the first electrode is mounted in a vehicle seat in the vehiclepassenger compartment.
 22. The vehicle passenger compartment proximitysensing system of claim 21 wherein the array of second electrodes ismounted adjacent a vehicle headliner in the vehicle passengercompartment.